Unable to get internet to work on MBP that is connected to WiFi

I have a MacBook pro that I'm having issues with. It connects to my home Wi-Fi (the n version of the Apple Airport Base Station) and I get a strong signal but whether I use Firefox or any other web browser or internet based program I get a message that I'm not connected to the internet.
I can even select network diagnostics and it walks me through steps where I choose my network, reset my cable modem, base station, etc. and at the end it says it is unable to fix the problem.
i have a 2nd MBP that I use on the same network with no issues at all. This issue started showing up about a month ago but did not happen often. Most of the time it happened when I had shut my MBP down since I had to go take it with me to meetings. Often after removing the battery for a minute I could boot up and it would work but now no matter what I do it won't work.
Any ideas of what could be causing this? I know I may have to go to the genius bar to have this looked at but hope to avoid it. Is there any other troubleshooting I can do? Thanks for your help.

Have you tried moving around? My MBP 15 is the first laptop ever that does not work on my desk but still gives me full wifi signal strength and no actual data coming through. I ended up having to relocate my access point...

I just tried it at a neighbor's house today on his wi-fi which is actually unprotected and it still didn't work so seems it's related to the MBP, not my Wi-Fi. Also, that involved moving it around a lot so seems that didn't resolve it either. Is it possible it's a hardware problem?

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